The book only costs $12.49 - the coupon works on books that are more expensive than that.

I am running out of classic books that I'm interested in that the code works on. Surely it's time to let us use the 'free classic book' code to work on any classic, public domain book? Or at least on any classic book below a certain price?

If you are referring to the codes for free books related to your Faithlife Connect subscription (which is the subject of this thread), then you should be aware that you don't "receive" (by email) any codes. Rather, you get the codes from your benefits page. Click HERE, then click on "ebooks." This is what you will do on the first day EVERY month.